Closed-cell polyisocyanate-based foams are widely used for insulation purposes, for example, in building construction and in the manufacture of energy efficient electrical appliances. In the construction industry, polyurethane (polyisocyanurate) board stock is used in roofing and siding for its insulation and load-carrying capabilities. Poured and sprayed polyurethane foams are widely used for a variety of applications including insulating roofs, insulating large structures such as storage tanks, insulating appliances such as refrigerators and freezers, insulating refrigerated trucks and railcars, etc.
All of these various types of polyurethane foams require blowing (expansion) agents for their manufacture. Insulating foams depend on the use of halocarbon blowing agents, not only to foam the polymer, but primarily for their low vapor thermal conductivity, a very important characteristic for insulation value. Historically, polyurethane foams used CFCs (chlorofluorocarbons, for example CFC-11, trichlorofluoromethane) and HCFCs (hydrochlorofluorocarbons, for example HCFC-141b, 1,1-dichloro-1-fluoroethane) as the primary blowing agent. However, due to the implication of chlorine-containing molecules such as the CFCs and HCFCs in the destruction of stratospheric ozone, the production and use of CFCs and HCFCs has been restricted by the Montreal Protocol. More recently, hydrofluorocarbons (HFCs), which do not contribute to the destruction of stratospheric ozone, have been employed as blowing agents for polyurethane foams. An example of an HFC employed in this application is HFC-245fa (1,1,1,3,3-pentafluoropropane).
A second type of insulating foam is thermoplastic foam, primarily polystyrene foam. Polyolefin foams (polystyrene, polyethylene, and polypropylene) are widely used in insulation and packaging applications. These thermoplastic foams were generally made with CFC-12 (dichlorodifluoromethane) as the blowing agent. More recently HCFCs (HCFC-22, chlorodifluoromethane) or blends of HCFCs (HCFC-22/HCFC-142b) or HFCs (HFC-152a) have been employed as blowing agents for polystyrene.
A third important type of insulating foam is phenolic foam. These foams, which have very attractive flammability characteristics, were generally made with CFC-11 (trichlorofluoromethane) and CFC-113 (1,1,2-trichloro-1,2,2-trifluoroethane) blowing agents
In addition to closed-cell foams, open-cell foams are also of commercial interest, for example in the production of fluid-absorbent articles. U.S. Pat. No. 6,703,431 (Dietzen, et. al.) describes open-cell foams based on thermoplastics polymers that are useful for fluid-absorbent hygiene articles such as wound contact materials. U.S. Pat. No. 6,071,580 (Bland, et. al.) describes absorbent extruded thermoplastic foams which can be employed in various absorbency applications. Open-cell foams have also found application in evacuated or vacuum panel technologies, for example in the production of evacuated insulation panels as described in U.S. Pat. No. 5,977,271 (Malone). Using open-cell foams in evacuated insulation panels, it has been possible to obtain R values of 10 to 15 per inch of thickness depending upon the evacuation or vacuum level, polymer type, cell size, density, and open cell content of the foam. These open-cell foams have traditionally been produced employing CFCs, HCFCs, or more recently, HFCs as blowing agents.
Multimodal foams are also of commercial interest, and are described, for example, in U.S. Pat. No. 6,787,580 (Chonde, et. al.) and U.S. Pat. No. 5,332,761 (Paquet, et. al.). A multimodal foam is a foam having a multimodal cell size distribution, and such foams have particular utility in thermally insulating articles since they often have higher insulating values (R-values) than analogous foams having a generally uniform cell size distribution. These foams have been produced employing CFCs, HCFCs, and, more recently, HFCs as the blowing agent.
As discussed above, the production of various types of foams historically employed CFCs as the blowing agent. In general, the CFCs produce foams exhibiting good thermal insulation, low flammability and excellent dimensional stability. However, despite these advantages the CFCs have fallen into disfavor due to their implication in the destruction of stratospheric ozone, as well as their implication in contributing to global warming.
HCFCs have been proposed as CFC substitutes, and are currently employed as foam blowing agents. However, the HCFCs have also been shown to contribute to the depletion of stratospheric ozone, and as a result their use has come under scrutiny, and the widespread use of HCFCs is scheduled for eventual phase out under the Montreal Protocol.
More recently HFCs have been proposed and employed as foam blowing agents. The HFCs do not contribute to the destruction of stratospheric ozone, but are of concern due to their contribution to the “greenhouse effect”, i.e., they contribute to global warming. As a result of their contribution to global warming, the HFCs have come under scrutiny, and their widespread use may also be limited in the future.
Hydrocarbons have also been proposed as foam blowing agents. However, these compounds are flammable, and many are photochemically reactive, and as a result contribute to the production of ground level ozone (i.e., smog). Such compounds are typically referred to as volatile organic compounds (VOCs), and are subject to environmental regulations.
There is need for producing foams that provide low flammability, good thermal insulation and high dimensional stability by using a blowing agent that has substantially no ozone depletion potential (ODP) and no or very low global warming potential (GWP).
There is also need to provide a process for producing plastic foams employing a blowing agent which has significantly less photochemical reactivity than the hydrocarbons, and hence does not contribute to the formation of ambient ozone and ground level smog.